Field of the Invention
The invention relates to a method for tripping a restraint device in a vehicle.
A configuration for tripping a restraint device in a vehicle is disclosed in European Patent EP 0 471 871 B1. The configuration includes an evaluation device, disposed centrally in the vehicle, in which a collision signal furnished by a sensor device is evaluated. The configuration also has ignition devices, distributed around the vehicle which are connected via one or more lines to the evaluation device. The evaluation device furnishes coded signals to the ignition devices. Each ignition device is electrically connected to an ignition element of a restraint device (i.e. air bag, seat belt tightener). Depending on the signals furnished by the evaluation device, the ignition element associated with the ignition device is acted upon by energy from an ignition capacitor of the ignition device, and thus trips the associated restraint device.
A coded signal transmitted by the evaluation device to the ignition device may contain more than merely a tripping command for igniting the ignition element. Such a signal can at the same time contain a challenge signal to the ignition device or other information, for instance about the electrical status of the evaluation device. A coded signal transmitted by the ignition device to the evaluation device may at the same time contain information about the electrical status of the ignition device, for instance about the ignition voltage applied to the ignition element via a controllable switch device, or about the ignition element resistance itself.
Each coded signal that is transmitted between the evaluation device and the ignition device in the forward or return direction will hereinafter be called an information signal. Only a tripping signal, which is transmitted from the evaluation device to the ignition device for igniting the ignition element, is singled out from the set of information signals.
When it is functioning properly the configuration is continuously monitored for operability. The medium for message transmission between the evaluation device and the ignition device, typically, an electrical line and in particular a two-wire line, a bus that connects a plurality of ignition devices to the evaluation device, an optical fiber, or a medium for wireless data transmission may be burdened by a high data throughput, especially if a plurality of ignition devices exchange data with the evaluation device.
If the evaluation device detects the necessity for tripping one or more restraint devices from a collision signal furnished by a sensor device, a tripping signal is sent to the affected ignition device. If at the moment of the demand for tripping the transmission medium is blocked because of a high throughput of information signals, then there is the risk that a tripping signal generated by the evaluation device cannot be transmitted quickly enough to the affected ignition device. The transmission time between the evaluation device and the ignition device plays an even greater role, the shorter the time period (commencing with the collision) within which the restraint device must be tripped. For tripping a side air bag, for instance, the period is approximately 5 msec long. In such time-critical applications, care must particularly be taken therefore to assure that the tripping signal after being generated in the evaluation circuit can be imposed on the medium without delay and transmitted to the ignition device. Delayed transmission of the tripping signal between the evaluation device and the ignition device causes late tripping of the restraint device and may lead to passenger injuries.